LEGO MINDSTORMS NXT Lab 4

Transcription

1 LEGO MINDSTORMS NXT Lab 4 This lab session is an introduction to wireless communication using the Lego Mindstorm NXT software. Two Tribots will speak to each other using a machine language or protocol called Bluetooth. Bluetooth is a wireless technology commonly used in cell phones, headsets, PDAs, laptops, and other portable devices to exchange information without the use of cables. Although its range is limited, it offers a means to communicate with devices using only a small amount of power. The beginning of this lab contains instructions on how to establish a Bluetooth connection between two Tribots. After establishing a connection, there will be step by step instructions on how to make one Tribot mimic the moves of the other. The final part of the lab is a challenge to create a remote control for one of the robots. Lab Summary A. Use the Lego Mindstorm NXT Help to setup a Bluetooth connection B. Develop code that will send Bluetooth messages C. Develop code that will receive Bluetooth messages D. (Challenge) Use one NXT robot as a remote control for the other robot Select another team that has a Tribot. Both teams will complete part A, and parts B and C will be split between the two teams. Part B focuses on developing code to send Bluetooth messages, and part C will show how to receive the messages. The code sending Tribot will be be called Big Brother, and the receiving code Tribot will called Little Brother. Part A) Setup a Bluetooth Connection Between Two Tribots 1) Select Help >> Contents and Index from the top of the NXT software Window 2) Instructions on how to establish a Bluetooth connection between two Tribots is explained in the Configuring the NXT for Wireless Communication section of the Receive Message block help. The Receive Message block help is found in the Action blocks section of the Contents view of the help as shown below: 3) Decide which robot will be the master (Big Brother) by creating the connection with it. The slave robot (Little Brother) will automatically configure itself for the connection. 4) Make the connection number 1 between the robots NXT Lab 4 Page 1/6

2 Part B) Big Brother 1) Select your profile under the User Profile drop-down box 2) Select File >> New to create a new program 3) Save it as Big Brother.rbt 4) Make sure that the Complete palette view is selected on the left 5) Place a Loop block found in the Flow palette onto the sequence beam 6) Configure the Loop block as 7) Place a Send Message block found in the Action palette inside the loop, and configure it as This is configuring Big Brother to send the text message Forward to Little Brother s first mailbox. 8) Place a Move block from the Flow palette after the Send Message block, and configure it as 9) Place another Send Message block after the Move block, and repeat step 7) with the text message Left. 10) Place a Move block after the recently placed Send Message block, and configure it as NXT Lab 4 Page 2/6

3 11) Repeat steps 7) and 8). Make sure the new blocks are placed after the turn left Move block from step 9). Hint: Use the copy and paste tools to save time. 12) Place another Send Message block, and have it send a text command Right 13) Place another Move block, and configure it as 14) Repeat steps 7) and 8). Make sure the new blocks are placed after the turn right Move block from step 14). 15) Use another Send Message block to send a Spin command. 16) Place and configure another Move block for spinning as The final program for Big Brother should look something like this: Tip: You can add comments to your code by double-clicking anywhere in the blank space and typing your comment. This practice greatly improves the readability of code, and is highly recommended for programming. 17) Save the Program and download it to one of the Tribots that will be used as Big Brother. 18) Proceed to the end of Part C) in this lab. Part C) Little Brother 1) Select File >> New to create a new program 2) Save it as Little Brother.rbt 3) Select the Complete palette view on the left 4) Place a Loop block found in the Flow palette onto the sequence beam, and configure it as NXT Lab 4 Page 3/6

4 5) Place a Receive Message block found in the Sensor palette inside the loop, and configure it as This block will be used to listen for commands being sent from Big Brother via Bluetooth wireless. 6) Place a Switch block found in the Flow palette after the Receive Message block, and configure it to switch between five different text values as Important: Make sure to uncheck Flat View before adding additional cases. Be sure to make Terminate the default case by clicking on the asterisk button in the lower right corner of the configuration window while the Terminate case is highlighted. This will ensure that if any other text message is received other than the ones in the list, the Terminate case will be executed as default. This will prevent the Tribot from moving when an odd text message is received. 7) Place a Move block inside the Forward case of the Switch block, and configure it to move forward as 8) Place another Move block in the Left case of the Switch, and configure it as NXT Lab 4 Page 4/6

5 9) Place another Move block inside the Right case of the Switch, and configure it as 10) Place another Move block inside the Spin case of the Switch, and configure it as 11) Wire the Text Out output of the Receive Message block to the Value input of the Switch block. 12) Place Display blocks at the beginning of each case to see what command is being processed by Little Brother. 13) Configure each Display block to display Forward, Left 02, Right 02, Rotation, and Stop 01 images respectively in the appropriate cases of the Switch. Use a position setting of 45 for X and 25 for Y to center the images with the exception of the Stop 01 image which will use 25 for X and 8 for Y. 14) The finished program should look similar to the following: Tip: You can add comments to your code by double-clicking anywhere in the blank space and typing your comment. This is how the F L R S comments were added to describe the tabs in NXT Lab 4 Page 5/6

6 the Switch block without having to navigate through them. This practice greatly improves the readability of code, and is highly recommended for programming. Note: Whenever images or sounds are used in a program, the images and sound files must also be downloaded to the NXT block, which takes up additional space. 15) Save the program, and download it to the Little Brother Tribot. =================END PARTS B AND C================== Start Little Brother first, and then start Big Brother. Notice that Little Brother will imitate Big Brother s behavior, and display the received commands on the NXT block window. Press the square, orange Enter buttons on the NXT blocks to stop the programs. Part D) (Challenge) Use One Tribot as a Remote Control for the Other Tribot One of the unique benefits of having Bluetooth capability is to create a remote control out of a Tribot that will control another Tribot. As an example, rotating a wheel will change the position indicator on the rotational sensor, and this value can be passed to the other Tribot for movement. The objective of this challenge is to create a remote control out of one Tribot that can control another Tribot to perform the following commands: Left and right turns Throttle for speed in at least the forward direction On/off switch Horn Reverse Here is a suggested plan of attack for this challenge: 1. Briefly research some other remote control designs for ideas 2. Decide which features of the Tribot will be used to perform each command 3. Use a flow chart to organize the overall architecture of the program 4. Create a skeleton of the program before writing in the functions. Use temporary flags (i.e. Sound blocks) to test the skeleton code. 5. Once the structure of the code is working properly, fill in the holes with final code operations Bonus! Try to control two or more Tribots using only a single remote control. Good Luck! NXT Lab 4 Page 6/6